How to center the link text within the button - any suggestions?

Relevant CSS

div { height:120px; width:120px; background-color:#ff8000; border-radius:50%; margin:auto; text-align:center; border:black 1px solid;

}

span { font-family:Vivaldi; font-size:30px; font-weight:bold; }

a{ text-decoration:none; color:#08298a; }

Relevant HTML

<div>
        <a href="http://www.mister-button.de/">Right on the <span>button</span></a>
    </div>